Optical health monitoring for aircraft overheat and fire detection systems

ABSTRACT

Overheat and fire detection for aircraft systems includes an optical controller and a fiber optic loop extending from the optical controller. The fiber optic loop extends through one or more zones of the aircraft. An optical signal is transmitted through the fiber optic loop from the optical controller and is also received back at the optical controller. The optical controller analyzes the optical signal to determine the temperature, strain, or both experienced within the zones.

CROSS-REFERENCE INFORMATION

This application claims the benefit of U.S. Provisional Application No.62/338,775 filed May 19, 2016 for “OPTICAL HEALTH MONITORING FORAIRCRAFT OVERHEAT AND FIRE DETECTION SYSTEMS” by Christopher Wilson,David William Frasure, Mark Thomas Kern, Mark Sherwood Miller, ScottKenneth Newlin, Chris George Georgoulias, Stefan Coreth and Ken Bell.

BACKGROUND

This disclosure relates generally to aircraft system health monitoringfor overheat and fire detection systems. More particularly, thisdisclosure relates to aircraft system health monitoring using opticalsignals.

Overheat detection systems monitor various zones within an aircraft,such as bleed ducts where high temperature, high pressure air is bledfrom the compressor stage of an engine, or in the wheel well of anaircraft to sense overheated brakes and/or “hot” tires which indicatethat the tire has a low air pressure or that the brakes are hot.Overheat detection can be used for any equipment on the aircraft thatrequires monitoring for overheat conditions, such as electric motors,compressors, etc. Bleed air is utilized for a variety of functions onthe aircraft, such as engine and airframe anti-icing, internal coolingof the engine, cabin pressurization and environmental controls,pressurization of hydraulic reservoirs and seals, and others. The bleedair typically has a temperature between 100° F. and 1,100° F. dependingon the distance that the bleed air has traveled from the engine. Thehigh temperature and pressure of the bleed air means that the bleed airmay damage the aircraft if a leak or rupture occurs in the bleed duct.As such, overheat detection systems have sensors that run the length ofthe bleed ducts, or along structures in the vicinity of the bleed ducts,to monitor for temperature changes that would indicate leaks or rupturesin the duct.

Prior art overheat detection systems typically utilize eutectic salttechnology to sense an overheat event. The eutectic salt surrounds acentral conductor and the eutectic salt is surrounded by an outersheath. A monitoring signal is sent down the central conductor, andunder normal operating conditions the eutectic salt operates as aninsulator such that no conduction occurs between the central conductorand the outer sheath. When an overheat event occurs, however, a portionof the eutectic salt melts and a low-impedance path is formed betweenthe central conductor and the outer sheath. The low-impedance path issensed by an electronic controller, which generates an overheat alarmsignal. When the overheat event has subsided, the eutectic saltre-solidifies and once again insulates the central conductor. Throughthe use of various salts to create a eutectic mixture, a specificmelting point for the salt can be achieved; thereby allowing differenteutectic salts to be used in different areas of the aircraft to provideoverheat monitoring across a variety of temperatures. While the eutecticsalt technology allows for overheat events to be detected, the eutecticsalt technology merely provides a binary indication of whether anoverheat event has or has not occurred.

SUMMARY

In one example, a system for an aircraft that includes a plurality ofzones includes a first zone fiber optic cable routed through a first setof the plurality of zones; a first local controller configured toprovide a first optical signal to the first zone fiber optic cable andobtain a first response signal from the first zone fiber optic cable;wherein the first local controller is further configured to determine atleast one temperature for each of first set of the plurality of zonesbased on the first response signal and provide an indication for firstdetected zones of the first set of the plurality of zones in which theat least one temperature is greater than a threshold value.

In another example, a method of detecting thermal conditions for anaircraft includes emitting, by a first local controller, a first opticalsignal to a first zone fiber optic cable, wherein the first zone fiberoptic cable is routed through each of a first plurality of zones of theaircraft; receiving, by the first local controller, a response signalfrom the first zone fiber optic cable based upon the first opticalsignal; determining, using the first local controller, at least onetemperature each of the first plurality of zones based on the responsesignal; and indicating a first condition for a respective one of thefirst plurality of zones if the at least one temperature for therespective one of the first plurality of zones is greater than athreshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an overheat detection system architecturefor monitoring all zones.

FIG. 2A is a schematic view of an overheat detection system architecturefor monitoring individual zones.

FIG. 2B is an enlarged view of a first embodiment of detail Y in FIG. 2Aincluding a dual loop configuration.

FIG. 2C is an enlarged view of a second embodiment of detail Y in FIG.2A including a probe configuration.

FIG. 2D is an enlarged view of a third embodiment of detail Y in FIG. 2Aincluding a reference configuration.

FIG. 3 is a schematic view of an overheat detection system architecturefor monitoring multiple zones.

FIG. 4 is a flow diagram depicting an overheat detection process.

FIG. 5 is a flow diagram depicting an overheat detection process.

DETAILED DESCRIPTION

FIG. 1 is a schematic view of overheat detection system 10 for aircraft12. Aircraft 12 includes zones Za-Zj and avionics controller 14.Overheat detection system 10 includes optical controller 16 and fiberoptic loop 18. Optical controller 16 includes optical transmitter 20,optical receiver 22, and computer-readable memory 24. Fiber optic loop18 includes first fiber optic cable 26. First fiber optic cable 26includes first end 28 and second end 30. Fiber optic loop 18 isconnected to optical controller 16 and extends between opticaltransmitter 20 and optical receiver 22. Both first end 28 and second end30 of first fiber optic cable 26 can be connected to optical transmitter20. Similarly, both first end 28 and second end 30 of first fiber opticcable 26 can be connected to optical receiver 22. It is understood,however, that in some examples only one of first end 28 or second end 30is connected to optical transmitter 20 and/or optical receiver 22. Firstfiber optic loop 18 extends through all zones Za-Zj of aircraft 12.Optical controller 16 is connected to avionics controller 14 tocommunicate with other systems within aircraft 12.

Optical controller 16 may be configured to control optical transmitter20 to control the transmission of an optical signal through fiber opticloop 18. Optical controller 16 may also be configured to receive anoptical signal from optical receiver 22 and to analyze the opticalsignal received at optical receiver 22. Optical controller 16 may be amicroprocessor, microcontroller, application-specific integrated circuit(ASIC), digital signal processor (DSP), field programmable gate-array(FPGA) or any other circuit capable of controlling optical transmitter20 and receiving signals from optical receiver 22. Optical controller 16may include one or more computer-readable memory encoded withinstructions that, when executed by the controller 16, cause opticalcontroller 16 and/or other elements of overheat detection system 10 tooperate in accordance with techniques described herein. Opticalcontroller 16 may further communicate with avionics controller 14 tocommunicate temperature data to avionics controller 14 using a wired orwireless connection. It is understood that all communications foroverheat detection system 10 can be made using wired, wireless, oroptical communications or some combination of these methods.

Computer-readable memory 24 of optical controller 16 can be configuredto store information within optical controller 16 during and afteroperation. Computer-readable memory 24, in some examples, can bedescribed as a computer-readable storage medium. In some examples, acomputer-readable storage medium can include a non-transitory medium.The term “non-transitory” can indicate that the storage medium is notembodied in a carrier wave or a propagated signal. In certain examples,a non-transitory storage medium can store data that can, over time,change (e.g., in RAM or cache). In some examples, computer-readablememory 24 can include temporary memory, meaning that a primary purposeof the computer-readable memory is not long-term storage.Computer-readable memory 24, in some examples, can be described as avolatile memory, meaning that the computer-readable memory 24 does notmaintain stored contents when electrical power to optical controller 16is removed. Examples of volatile memories can include random accessmemories (RAM), dynamic random access memories (DRAM), static randomaccess memories (SRAM), and other forms of volatile memories. In someexamples, computer-readable memory 24 can be used to store programinstructions for execution by one or more processors of opticalcontroller 16. For instance, computer-readable memory 24 can be used bysoftware or applications executed by optical controller 16 totemporarily store information during program execution.

Optical controller 16 is connected to optical transmitter 20 to controlthe transmission of an optical signal from optical transmitter 20 tofiber optic cable 18. Optical controller 16 is also connected to opticalreceiver 22 to analyze the signals received by optical receiver 22.Optical controller 16 receives information regarding the optical signalfrom optical receiver 22. Variations in the optical signals analyzed byoptical controller 16 allows optical controller 16 to determine thetemperature within zones Za-Zj and to determine the location that atemperature variation occurs in within zones Za-Zj. The variations inthe optical signals also allow optical controller 16 to determine thestrain experienced at various locations along fiber optic cable 26.

Optical transmitter 20 is controlled by optical controller 16 and can beconnected to first end 28 of fiber optic cable 26, to second end 30 offiber optic cable 26, or to both. Optical transmitter 20 is configuredto provide an optical signal to first end 28 or second end 30 of firstfiber optic cable 26. Optical transmitter 20 may be any suitable opticalsource for providing an optical signal to first fiber optic cable 26.For example, optical transmitter may be a light-emitting diode or alaser. It is further understood that optical transmitter 20 may beconfigured to provide the optical signal in any suitable manner, such asthrough a single pulse at a fixed wavelength; a tunableswept-wavelength; a broadband signal; and a tunable pulse. Furthermore,while optical controller 16 is described as including opticaltransmitter 20, it is understood that optical controller 16 may includeone or more optical transmitters 20 to provide optical signals to firstfiber optic cable 26.

Optical receiver 22 is configured to receive the optical signal fromeither first end 28 or second end 30 of first fiber optic cable 26.Where optical transmitter 20 provides the optical signal through firstend 28, a first portion of the optical signal travels through firstfiber optic cable 26 and is received by optical receiver 22 at secondend 30. A second portion of the optical signal can be reflected back tofirst end 28 and received by optical receiver 22. Optical receiver 22communicates information regarding the first portion of the opticalsignal, the second portion of the optical signal, or both to opticalcontroller 16. Optical receiver 22 may be any suitable receiver forreceiving an optical signal. For example, optical receiver 22 may be aphotodiode, a photodiode array, a phototransistor, or any other suitableoptical receiving device.

Fiber optic loop 18 may include a single, continuous fiber optic loopextending through all zones Za-Zj in aircraft 12. Zones Za-Zj mayinclude any location on aircraft 12 where overheat detection is desired.For example, zones Za-Zj may include bleed air ducts, cross-over bleedair ducts, wheel wells, wing boxes, Air Conditioning (A/C) packs,anti-icing systems, nitrogen generation systems, or any other area wheretemperature sensing is desirable. Zones Za-Zj may be divided andassigned in any desired manner. In the illustrated example, zone Zaincludes right side cross-over bleed air duct 32 a and left sidecross-over bleed air duct 32 b; zone Zb includes right wing box 34 a;zone Zc includes right pylon 36 a; zone Zd includes right wing iceprotection system 38 a; zone Ze includes rights A/C pack 40 a, left A/Cpack 40 b, right wheel well 42 a, and left wheel well 42 b; zone Zfincludes first APU 44 a; zone Zg includes second APU 44 b and third APU44 c, zone Zh includes left wing box 34 b; zone Zi includes left pylon36 b; and zone Zj includes left wing ice protection system 38 b. Whileaircraft 12 is described as including ten zones, it is understood thataircraft 12 may be divided into as many or as few zones as desired.

Aircraft 12 may be divided into zones in any desired manner; forexample, aircraft 12 may be divided into zones based on the overheattemperature for the components located in that zone or based on systemtype. Each zone Za-Zj of aircraft may have a different alarm set point,such that where the temperature in zone Za is the same as thetemperature in zone Zb an overheat alarm may be triggered for zone Zbbut not for zone Za.

Fiber optic loop 18 is a continuous fiber optic loop that passes throughall zones Za-Zj of aircraft 12 to provide temperature and/or strainsensing across all zones Za-Zj. Fiber optic loop 18 is connected tooptical controller 16, and optical controller 16 is configured todetermine the occurrence of an overheat event, the zone in which theoverheat event has occurred in, and whether the overheat event is at orabove the alarm set point for that zone. Optical controller 16 thusknows the length and alarm set point of fiber optic loop 18 in each zoneZa-Zj and the order in which fiber optic loop 18 passes through eachzone Za-Zj. While overheat detection system 10 is described as includingfiber optic loop 18, overheat detection system 10 may include anydesired number of fiber optic loops passing through each zone 18. Forexample, overheat detection system 10 may include a second fiber opticloop connected to optical controller 16 such that an overheat conditionis triggered only when both first fiber optic loop 18 and the secondfiber optic loop go into an alarm condition within a specified timeperiod. Moreover, while fiber optic loop 18 is described as includingfirst fiber optic cable 26 in a loop configuration, it is understoodthat first fiber optic cable 26 can be disposed in a single-endedconfiguration such that only one of first end 28 and second end 30 isconnected to optical controller 16. For example, in the single-endedconfiguration where first end 28 is connected to optical controller 16,optical controller 16 can provide an optical signal to first end 28 offirst fiber optic cable 26 and can interpret the signal that isreflected back to optical controller 16 through first end 28.

Optical controller 16 analyzes the information provided by the opticalsignal using the techniques discussed herein to determine thetemperature in each zone Za-Zj, the strain in each zone Za-Zj, or both.Where optical controller 16 determines that the temperature in a zone isabove the alarm set point for that zone, optical controller 16 generatesan alarm signal that an overheat event has occurred. In addition tosensing the existence of an overheat event, monitoring the temperaturein each zone Za-Zj allows overheat detection system 10 to provide firedetection for zones Za-Zj. For example, a dramatic, sudden increase intemperature can indicate the existence of a fire or overheat event, andbecause optical controller 16 monitors the actual temperature instead ofmerely whether or not an overheat event has occurred, optical controller16 can sense the dramatic, sudden increase in temperature and provide afire or overheat detection warning to the cockpit, to a fire suppressionsystem, or to any other location.

Overheat detection system 10 can sense a temperature or strain at anylocation or at multiple locations along first fiber optic cable 26.Because the temperature can be sensed at any location or multiplelocations along first fiber optic cable 26, a temperature profile may bedeveloped for the entire length of first fiber optic cable 26, and assuch, a temperature profile may be developed for each zone Za-Zj.Overheat detection system 10 can further provide locational informationregarding the exact location within each zone Za-Zj that an event occursat. The temperature profile for each zone Za-Zj can then be compared toa maximum allowable temperature profile, which can include a singletemperature for an entire zone Za-Zj or multiple temperatures at varyinglocations in each zone Za-Zj. As such, it is understood that opticalcontroller 16 can determine any desired temperature data for any zoneZa-Zj, and the temperature data can include a single temperature at asingle location within a zone, temperatures at multiple locationsthroughout a zone, a temperature profile for a zone, or determining anddeveloping any other desired temperature data for the zone.

Optical controller 16 can also generate trend data to allow for healthmonitoring of aircraft 12. The trend data may include data regardingtemperature trends, strain trends, or both. The trend data can be storedin memory 24 of optical controller 16 or in any other suitable storagemedium at any other suitable location, such as the memory of avionicscontroller 14. It is understood that the data can be monitored in realtime. For example, optical controller 16 may communicate with adedicated health monitoring system to monitor the temperature data inreal time. The stored trend data provides statistical and historicaldata for the temperature, strain, or both experienced in all zonesZa-Zj. The temperature trend data may be stored and monitored bymaintenance personnel. As such, the temperature trend data allowsmaintenance personnel to determine the exact location of progressivetemperature increases over time. It is further understood that opticalcontroller 16 can generate the exact location of a one-time temperaturevariation, strain variation, or both. Generating the locations ofprogressive temperature increases allows for preventative, targetedmaintenance before a failure occurs. For example, the temperature trendin right wheel well 42 a may be monitored to generate trend data. Thetrend data may show that a tire within right wheel well 42 a exceeds thenormal operating temperatures without reaching the alarm set point. Insuch a case an overheat event does not occur; however, the temperaturetrend data informs maintenance personal that the tire may be close tofailing or that the tire may be low on air pressure and that amaintenance action is required. Similar to temperature monitoring, thestrain trend data may be stored and areas of increased strain may belocated. For example, the pressure of the bleed air passing throughright side cross-over bleed duct 32 a may impart a strain on the wall ofright side cross-over bleed duct 32 a. The level of the strain and thelocation of the strain may be detected by optical controller 16analyzing the information received from the optical signals. The straininformation may then be communicated to ground personnel and used toinvestigate the location of the increased strain to determine anymaintenance action that should be taken.

Optical controller 16 is connected to avionics controller 14 tocommunicate information to avionics controller 14. While opticalcontroller 16 is described as communicating with avionics controller 14,optical controller 16 may communicate with aircraft 12 and withmaintenance personnel in any suitable manner. Optical controller 16 mayalso communicate directly with a cockpit of aircraft 12 to provideoverheat or fire detection warning, or to indicate that maintenance isnecessary. Optical controller 16 may further communicate temperaturedata to other non-overheat detection system computers, which maycommunicate an overheat status to the cockpit. Aircraft 12 may alsoinclude a central overheat detection system computer that communicateswith various overheat detection systems on aircraft, and the centraloverheat detection system computer may communicate any overheat statusfrom any overheat detection system to the cockpit. It is understood thatall communications for overheat detection system 10 can be made usingwired, wireless, or optical communications or some combination of thesemethods.

FIG. 2A is a schematic diagram of overheat detection system 10′ foraircraft 12. Aircraft 12 includes zones Za-Zj and avionics controller14. Overheat detection system 10′ includes optical controllers 16 a-16 jand fiber optic loops 18 a-18 j. Zones Za-Zj extend through any portionof aircraft 12 where temperature monitoring, strain monitoring, or bothare desirable.

In overheat detection system 10′, each optical controller 16 a-16 j andfiber optic loop 18 a-18 j is dedicated to a single zone Za-Zj. As such,each optical controller 16 a-16 j and fiber optic loop 18 a-18 jmonitors and gathers temperature and strain information from a singlezone Za-Zj. Each optical controller 16 a-16 j includes an opticaltransmitter (discussed in detail below in FIGS. 2B-2D) and an opticalreceiver (discussed in detail below in FIGS. 2B-2D).

All zones Za-Zj can have a unique alarm set point, and each zone Za-Zjcan include any location or combination of locations on aircraft 12where temperature and strain monitoring and detection are desired. Forexample, zones Za-Zj may include bleed air ducts, cross-over bleed airducts, wheel wells, wing boxes, A/C packs, anti-icing systems, nitrogengeneration systems, or any other area where temperature sensing isdesirable. While aircraft 12 is described as including ten zones, it isunderstood that aircraft 12 may be divided into as many or as few zonesas desired.

Fiber optic loop 18 d is illustrated as including first fiber opticcable 26 d, and first fiber optic cable 26 d includes first end 28 d andsecond end 30 d. It is understood, that while fiber optic loop 18 d isillustrated as including first fiber optic cable 26 d, each fiber opticloop 18 a-18 j can include one or more fiber optic cables. In addition,each fiber optic cable can include a first end and a second endconnected to controllers 16 a-16 j. Overheat and strain detection acrosseach of zones Za-Zj is substantially similar, and for ease ofdiscussion, zone Zd will be discussed in further detail. Opticalcontroller 16 d controls the transmission of an optical signal from theoptical transmitter through fiber optic loop 18 d. The optical signalmay be provided to first fiber optic cable 26 d through first end 28 d,second end 30 d or both. Where the optical signal is provided throughfirst end 28 d, a first, majority portion of the optical signal passesthrough first fiber optic cable 26 d, to second end 30 d, and isreceived by the optical receiver at second end 30 d. A second, minorityportion of the fiber optic signal is backscattered within first fiberoptic cable 26 d and received at first end 28 d by the optical receiver.While optical controller 16 d is described as including a single opticalreceiver, it is understood that optical controller 16 d may includemultiple optical receivers to receive the optical signal from differentfiber optic loops, different fiber optic cables, and/or different endsof the fiber optic cables. Optical controller 16 d receives opticalsignal data regarding both the first, majority portion and the second,minority portion of the optical signal. Optical controller 16 d analyzesthe optical signal data to determine the temperature, strain, or bothwithin zone Zd. Moreover, while optical controller 16 d is described asreceiving both the first portion and the second portion of the opticalsignal, it is understood that in some examples first end 28 d isconnected to optical controller 16 d while second end 30 d remainsdisconnected, such that fiber optic cable 26 d is in a single-endedconfiguration. Where fiber optic cable 26 d is in a single-endedconfiguration, optical controller 16 d can receive relevant informationfrom the backscattered portion of the optical signal.

FIG. 2B is an enlarged view of detail Y in FIG. 2A, showing a dual loopconfiguration. FIG. 2B includes optical controller 16 d, first fiberoptic loop 18 d, second fiber optic loop 46 d, optical transmitters 20d, optical receivers 22 d, and computer-readable memory 24 d. Firstfiber optic loop 18 d includes first fiber optic cable 26 d, and firstfiber optic cable 26 d includes first end 28 d and second end 30 d.Second fiber optic loop 46 d includes second fiber optic cable 48 d, andsecond fiber optic cable 48 d includes first end 50 d and second end 52d.

First fiber optic loop 18 d extends from optical controller 16 d throughzone Zd (best seen in FIG. 2A). First fiber optic loop 18 d includesfirst fiber optic cable 26 d, and first fiber optic cable 26 d isconfigured to receive a first optical signal from optical transmitter 20d. Optical receiver 22 d is configured to receive the first opticalsignal from first fiber optic cable 26 d. Optical receiver 22 d providesinformation regarding the resultant optical signal to optical controller16 d. Optical controller 16 d analyzes the information to generatetemperature information, strain information, or both.

Similar to first fiber optic loop 18 d, second fiber optic loop 46 dextends through zone Zd. Second fiber optic loop 46 d runs parallel tofirst fiber optic loop 18 d through zone Zd. Second fiber optic cablereceives a second optical signal from optical transmitter 20 d. Opticalreceiver 22 d receives the second optical signal from second fiber opticcable 48 d, and optical receiver 22 d provides information regarding thereceived second optical signal to optical controller 16 d. Opticalcontroller 16 d analyzes the information to generate temperatureinformation, strain information, or both.

While first fiber optic loop 18 d and second fiber optic loop 46 d areillustrated as receiving an optical signal from discrete opticaltransmitters 20 d, it is understood that a single optical transmittermay provide the same optical signal to both first fiber optic loop 18 dand second fiber optic loop 46 d.

First fiber optic loop 18 d and second fiber optic loop 46 d runparallel through zone Zd. First fiber optic loop 18 d and second fiberoptic loop 46 d extend through zone Zd in a dual loop configuration. Inthe dual loop configuration, the optical signal provided to second fiberoptic cable 48 d is preferably identical to the optical signal providedto first fiber optic cable 26 d. Providing the same optical signal toboth first fiber optic cable 26 d and second fiber optic cable 48 dallows optical controller 16 d to compare the resultant signal obtainedfrom first fiber optic cable 26 d to the resultant signal obtained fromsecond fiber optic cable 48 d, thereby providing a greater degree ofconfidence in both first fiber optic loop 18 d and second fiber opticloop 46 d. As such, the optical signals passing through first fiberoptic loop 18 d and second fiber optic loop 46 d provide data regardingthe same changes in temperature and strain at the same locationsthroughout first fiber optic loop 18 d and second fiber optic loop 46 d.Both first fiber optic cable 26 d and second fiber optic cable 48 dcommunicate the information regarding the resultant optical signals tooptical controller 16 d.

In a single loop configuration, a single fiber optic loop passes througheach zone, and an overheat event is indicated when optical controller 16d detects an alarm state in the single fiber optic loop. In a dual loopconfiguration, a first fiber optic loop passes through a zone and asecond fiber optic loop passes through the zone running parallel to thefirst fiber optic loop. An overheat event is detected when both thefirst fiber optic loop and the second fiber optic loop sense the sameoverheat event within a specified time duration. First fiber optic cable26 d and second fiber optic cable 48 d have the same alarm set point inthe same zone. An overheat event is detected when both first fiber opticcable 26 d and second fiber optic cable 48 d sense the overheat eventwithin a specified time duration. As such, optical controller 16 dtriggers an overheat alarm only when both first fiber optic cable 26 dand second fiber optic cable 48 d sense the overheat event in zone Zd,within a predetermined time period. In this way, the dual loopconfiguration ensures that overheat events are detected with highreliability. While a dual loop configuration is described as extendingthrough zone Zd, it is understood that a dual loop configuration maypass through any zone Za-Zj and be received by any optical controller 16a-16 j.

FIG. 2C is an enlarged view of detail Y of FIG. 2A, showing opticalcontroller 16 d including a probe signal configuration. In a probesignal configuration, an optical signal is provided to a first end of afiber optic cable and a probe signal is provided to a second end of thefiber optic cable. For example, the optical signal may be a pulsedsignal and the probe signal may be a continuous wave. The optical signalinteracts with the probe signal as the optical signal and the probesignal pass within the fiber optic cable. The interaction between theoptical signal and the probe signal provides information regarding thetemperature, the strain, or both along the length of the fiber opticcable. FIG. 2C includes optical controller 16 d, fiber optic loop 18 d,optical transmitter 20 d, optical receiver 22 d, computer-readablememory 24 d, probe transmitter 54 d, and probe receiver 56 d. Fiberoptic loop 18 d includes first fiber optic cable 26 d, and first fiberoptic cable 26 d includes first end 28 d and second end 30 d.

Fiber optic loop 18 d extends through zone Zd (best seen in FIG. 2A).First end 28 d of first fiber optic cable 26 d is connected to opticalcontroller 16 d and configured to receive an optical signal from opticaltransmitter 20 d. Second end 30 d of first fiber optic cable 26 d isconnected to optical controller 16 d and is configured to receive aprobe signal from probe transmitter 54 d. Optical controller 16 dcontrols both optical transmitter 20 d and probe transmitter 54 d.

Optical transmitter 20 d provides an optical signal to first end 28 d offirst fiber optic cable 26 d. Simultaneously, probe transmitter 54 dprovides a probe signal to second end 30 d of first fiber optic cable 26d. For example, one of the optical signal and the probe signal may be apulsed signal and the other one of the optical signal and the probesignal may be a continuous wave. The optical signal and the probe signalinteract as the optical signal passes the probe signal in first fiberoptic cable 26 d. A frequency difference between the optical signal andthe probe signal is received by optical receiver 22 d, probe receiver 56d, or both. Optical controller 16 d monitors the interaction between theoptical signal and the probe signal, as the interaction between theoptical signal and the probe signal changes as the temperature andstrain change within zone Zd. As such, optical controller 16 d monitorsthe interaction to determine the temperature, strain, or both alongfirst fiber optic cable 26 d. While optical controller 16 d is describedas including optical transmitter 20 d and probe transmitter 54 d, it isunderstood that any optical controller 16 a-16 j may include an opticaltransmitter and a probe transmitter to provide an optical signal and aprobe signal to first fiber optic cables 26 a-26 j (best seen in FIG.2A).

FIG. 2D is an enlarged view of detail Y of FIG. 2A, showing opticalcontroller 16 d in a reference configuration. In the referenceconfiguration, an optical signal is provided to a first fiber opticcable and a reference signal is provided to a reference fiber opticcable, which runs parallel to the first fiber optic cable. The opticalsignal and the reference signal are both received at an opticalcontroller and combined. The interaction of the optical signal with thereference signal creates an interference pattern, which can then beanalyzed to obtain temperature data, strain data, or both. FIG. 2Dincludes optical controller 16 d, fiber optic loop 18 d, opticaltransmitter 20 d, optical receiver 22 d, computer-readable memory 24 d,reference transmitter 58 d, and reference receiver 60 d. Fiber opticloop 18 d includes first fiber optic cable 26 d and reference fiberoptic cable 62 d. First fiber optic cable 26 d includes first end 28 dand second end 30 d. Similarly, reference fiber optic cable 62 dincludes first end 64 d and second end 66 d.

Fiber optic loop 18 d extends through zone Zd (best seen in FIG. 2A).First fiber optic cable 26 d and reference fiber optic cable 62 d runparallel through zone Zd. First end 28 d of first fiber optic cable 26 dis connected to optical controller 16 d and configured to receive anoptical signal from optical transmitter 20 d. Similarly, first end 64 dof reference fiber optic cable 62 d is connected to optical controller16 d and configured to receive a reference signal from referencetransmitter 58 d. While first fiber optic cable 26 d is described asreceiving an optical signal from optical transmitter 20 d and referencefiber optic cable 62 d is described as receiving a reference signal fromreference transmitter 58 d, it is understood that a single opticaltransmitter may provide both the optical signal to first fiber opticcable 26 d and the reference signal to reference fiber optic cable 62 d.

Second end 30 d of first fiber optic cable 26 d is connected to opticalcontroller 16 d to provide the optical signal to optical receiver 22 d.Similarly, second end 66 d of reference fiber optic cable 62 d isconnected to optical controller 16 d to provide the reference signal toreference receiver 60 d. It is understood that while second end 30 d offirst fiber optic cable 26 d provides the optical signal to opticalreceiver 22 d, a second optical receiver may be connected to first end28 d to receive any backscattering of the optical signal through firstend 28 d. Similarly, a second reference receiver may receive anybackscattering of reference signal through first end 64 d of referencefiber optic cable 62 d.

Optical controller 16 d receives both the optical signal and thereference signal and combines the optical signal and the referencesignal to generate an interference pattern. Optical controller 16 danalyzes the combined optical signal and reference signal to determinetemperature changes, strain changes, or both along fiber optic loop 18d. It is understood that optical controller 16 d can combine the opticalsignal received at second end 30 d with the reference signal received atsecond end 66 d, or can combine the backscattered optical signalreceived at first end 30 d with the backscattered reference signalreceived at first end 64 d. While fiber optic loop 18 d is described asincluding first fiber optic cable 26 d and reference fiber optic cable62 d, it is understood that any fiber optic loop 18 a-18 j may include afirst fiber optic cable and a reference fiber optic cable. As such, anyoptical controller 16 a-16 j may be configured to combine and analyze anoptical signal and a reference signal.

FIG. 3 is a schematic diagram of overheat detection system 10″ foraircraft 12. Aircraft 12 includes zones Za-Zj and avionics controller14. Overheat detection system 10″ includes optical controllers 16 a-16 cand fiber optic loops 18 a-18 c. Fiber optic loops 18 a-18 c includefirst fiber optic cables 26 a-26 c, and first fiber optic cables 26 a-26c include first ends 28 a-28 c and second ends 30 a-30 c.

In overheat detection system 10″ fiber optic loop 18 a passes throughzones Zb-Zd, and fiber optic loop 18 a is connected to opticalcontroller 16 a. Fiber optic loop 18 b passes through zones Za and Ze-Zgand fiber optic loop 18 b is connected to optical controller 16 b. Fiberoptic loop 18 c passes through zones Zh-Zj, and fiber optic loop 18 c isconnected to optical controller 16 c. As such, each fiber optic loop 18a-18 c passes through and gathers information regarding multiple zonesof aircraft 12.

Different systems within aircraft 12 require overheat detectionmonitoring, and each system may be divided into multiple zones. Forexample, a bleed air duct in aircraft 12 may include multiple zones witha single fiber optic loop extending through all of the zones of thebleed air duct. Each system may thus be divided into multiple zones andmay include a dedicated optical controller and fiber optic loop. It isunderstood, however, that aircraft 12 may be divided into zones in anydesired manner.

Optical controllers 16 a-16 c can communicate with avionics controller14, and avionics controller 14 can consolidate the information receivedfrom optical controllers 16 a-16 c and provide the information to thecockpit, provide the information to maintenance personnel, or store theinformation to generate trend data. While optical controllers 16 a-16 care described as communicating with avionics controller 14, it isunderstood that optical controllers 16 a-16 c can communicate directlywith the cockpit or ground personnel, can store the information togenerate trend data, and can communicate with a central overheatcomputer. It is understood that all communications for overheatdetection system 10 can be made using wired, wireless, or opticalcommunications or some combination of these methods.

Fiber optic loops 18 a-18 c are similar, and for purposes of clarity andease of discussion, fiber optic loop 18 a will be discussed in furtherdetail. Fiber optic loop 18 a passes through each of zones Zb-Zd and isconnected to optical controller 16 a. First fiber optic cable 26 areceives an optical signal from optical transmitter 20 a located withinoptical controller 16 a and transmits the optical signal to opticalreceiver 22 a located within optical controller 16 a. Optical controller16 a analyzes the signal received by optical receiver 22 a to determinethe temperature in zones Zb-Zd. Each zone Zb-Zd may have a differentalarm set point as the temperature resistance of each zone may differ.As such, optical controller 16 a analyzes the information received todetermine the temperature in each zone. In addition to determiningtemperature in zones Zb-Zd, optical controller 16 a can analyze theinformation received from first fiber optic cable 26 a to determine thestrain experienced in each zone Zb-Zd. Optical controller 16 a can thusmonitor temperature, strain, or both within zones Zb-Zd. While fiberoptic loop 18 a is described as including first fiber optic cables 26 ain a loop configuration, it is understood that first fiber optic cable26 a can be disposed in a single-ended configuration such that only oneof first end 28 a and second end 30 a is connected to optical controller16 a. For example, in the single-ended configuration where first end 28a is connected to optical controller 16 a, optical controller 16 a canprovide an optical signal to first end 28 a of first fiber optic cable26 a and can interpret the signal that is reflected back through firstend 28 a.

With continued reference to FIGS. 1-3, FIGS. 4-5 are flow diagramsillustrating example operations for determining the occurrence andlocation of an overheat event. For purposes of clarity and ease ofdiscussion, the example operations are described below within thecontext of overheat detection system 10.

FIG. 4 is a flow diagram illustrating example operations to provideoverheat detection in an aircraft utilizing optical signals. In step 68,an optical signal is provided to one or more fiber optic cables. Forexample, optical transmitter 20 can provide an optical signal to firstfiber optic cable 26 through first end 28, second end 30, or both offiber optic cable 26. In step 70, an optical response signal is receivedfrom the fiber optic cable. For instance, optical receiver 22 mayreceive the optical response signal from first fiber optic cable 26, andoptical receiver 22 may provide the optical response signal to opticalcontroller 16. In step 72, the optical response signal is analyzed todetermine the temperature, strain, or both along the fiber optic cable.For example, optical controller 16 may analyze the optical responsesignal received from optical receiver 22 to determine the actualtemperature and/or strain at various locations along first fiber opticcable 26. Optical controller 16 may use any suitable method to analyzethe optical response, such as the methods discussed below. It isunderstood that first fiber optic cable 26 may sense a temperature atany location along first fiber optic cable 26 and the optical signal canbe interrogated to determine the precise location that a temperaturechange occurs at. As such, the temperature data analyzed by opticalcontroller 16 may include information to determine a temperature at asingle location within a zone, a temperature at multiple locationsthroughout a zone, a temperature profile for a zone, or any othertemperature information for the zone. In step 74, the temperature dataand/or strain data generated in step 72 is compared against a threshold.Where the temperature data and/or strain data indicates that thetemperature and/or strain are below the threshold level, the operationreturns to step 68. Where the temperature data and/or strain dataindicates that the temperature and/or strain are above the thresholdlevel, the operation proceeds to step 76 and the existence of theoverheat condition is indicated and communicated to the cockpit and/orground personnel.

FIG. 5 is a flow diagram illustrating example operations using opticalsignals to provide health monitoring for an aircraft. In step 78, anoptical signal is provided to one or more fiber optic cables. In step80, an optical response signal is received from the fiber optic cable.In step 82, the optical response signal is analyzed to determine thetemperature, strain, or both experienced along the fiber optic cable. Instep 84, the temperature data, strain data, or both is stored in amemory. For example, temperature data may be stored in memory 24 ofoptical controller 16. In step 86, trends are developed for the storedtemperature data and/or strain data, and the trends are monitored forany patterns indicating that a maintenance action is necessary.

By utilizing fiber optic loop 18 to determine the existence of anoverheat event, prior art eutectic salt sensors, and therefore theelectrical connections associated with the eutectic salt sensors, may beeliminated from aircraft 12. The prior art eutectic salt sensors sensewhether an overheat event is or is not occurring, and as such provide abinary response. Unlike the prior art eutectic sensors, fiber optic loop18 senses any changes in temperature and the location of the temperaturechange, not merely whether a temperature set point has been exceeded. Assuch, optical controller 16 may gather trend data for each zone thatfiber optic loop 18 extends through, as data is continuously gathered byoptical controller 16. Temperature trend data provides information tomaintenance personnel regarding the overall health of each zone Za-Zj.Providing the trend data allows for maintenance to be performed atspecific, relevant locations and only when needed, thereby decreasingthe downtime of aircraft 12. In addition to providing temperature trenddata, fiber optic loop 18 is able to sense strain within each zoneZa-Zj, unlike the prior art eutectic salt sensors that are sensitive totemperature alone. Utilizing fiber optic loop 18 thus providesadditional structural information to maintenance personnel.

Monitoring the temperature trend, strain trend, or both within zonesZa-Zj provides information regarding the overall health of the zonebeing monitored, and of the system within which the zone is located. Thetrend data can be used to facilitate preventative maintenance. Moreover,monitoring the trend data allows for maintenance actions to be scheduledat a convenient time and location, instead of waiting until an actualfailure occurs, which leads to gate departure delay, cancelled flights,or in-flight crew action. In addition, monitoring the actual temperaturein zones Za-Zj enables overheat detection system 10 to provide firemonitoring in addition to overheat detection. A sudden, dramaticincrease in temperature can indicate the existence of a fire instead ofan overheat event. For example, a fire in a wheel well would cause asudden, dramatic increase in temperature in the wheel well, and thatsudden, dramatic increase would be sensed by the portion of the fiberoptic cable passing through the zone that includes the wheel well.Optical controller 16 can analyze the data provided from the zone thatincludes the wheel well to determine the existence of the fire event,and to communicate the existence of the fire event to the cockpit, to afire suppression system, or to any other appropriate system orpersonnel.

A variety of fiber optic cables and operating principles may be used todetermine the existence of an overheat event. For example, overheatdetection system 10 may utilize a single fiber optic cable, dual fiberoptic cables, and fiber optic cables including Bragg gratings. Moreover,the fiber optic cables may be arranged in a single loop configuration, adual loop configuration, or any other suitable configuration. An opticalsignal is initially provided to first fiber optic cable 26, and as theoptical signal travels through first fiber optic cable 26 the majorityof the optical signal travels from first end 28 to second end 30, but afraction of the optical signal is backscattered towards first end 28.Optical controller 16 can analyze the portion of the optical signalreceived through second end 30, the portion of the optical signalbackscattered through first end 28, or a combination of both todetermine temperature and/or strain information. As such, it is furtherunderstood that first fiber optic cable 26 can be arranged in asingle-ended configuration where one of first end 28 or second end 30 isconnected to optical controller 16. In a single-ended configuration,optical controller 16 can provide the optical signal through one end offirst fiber optic cable 26 and can interpret the portion of the opticalsignal backscattered through the end of first fiber optic cable 26connected to optical controller 16.

Where fiber optic loop 18 includes Bragg gratings, optical controller 16can analyze the optical signal using a variety of principles, includingWave Division Multiplexing (WDM), Time Division Multiplexing (TDM), acombination of WDM and TDM (WDM/TDM), and Coherent Optical FrequencyDomain Reflectometry (COFDR), among others. A Bragg grating is adistributed reflector within the fiber optic cable that is configured toreflect a particular wavelength of light and allow all other wavelengthsto pass through. As such, the Bragg gratings function aswavelength-specific reflectors. The specific wavelength reflected by aspecific Bragg grating is the Bragg wavelength. In overheat detectionsystem 10, fiber optic loop 18 includes various Bragg gratings withinfirst fiber optic cable 26. Different Bragg gratings may be disposedwithin different zones in the aircraft. As such, the Bragg wavelengthassociated with each zone differs from the Bragg wavelength associatedwith the other zones. Because optical controller 16 knows which Braggwavelength is associated with which zone, optical controller 16 maydetermine the distance to each Bragg grating based on the time taken forthe Bragg wavelength to travel from first end 28, to the Bragg grating,and back to first end 28. The Bragg wavelength is sensitive to bothstrain and temperature. Changes in strain and temperature result in ashift in the Bragg wavelength, which can be detected by opticalcontroller 16 and used to determine the change in strain and/ortemperature.

In WDM, optical controller 16 provides an optical signal to first end 28of first fiber optic cable 26 with optical transmitter 20. Opticaltransmitter 20 is preferably a tunable, swept-wavelength laser. Thewavelength of optical transmitter 20 is swept across a pre-definedrange. The wavelength of the optical signal being transmitted at anygiven moment in time is known. The Bragg wavelengths are received atfirst end 28 of first fiber optic cable 26 by optical receiver 22, andoptical controller 16 converts changes in the Bragg wavelengths intointensity vs. time. A shift in the Bragg wavelength indicates a changein temperature and/or strain, and tracking the changes in the Braggwavelength allows optical controller 16 to determine the temperature ateach Bragg grating within each zone Z₁-Z_(n).

In TDM, optical controller 16 provides an optical signal to first end 28of first fiber optic cable 26 with optical transmitter 20. In TDM,optical transmitter 20 is a broadband laser light source such that amultitude of wavelengths are transmitted through first fiber optic cable26. Each Bragg grating is configured to reflect a particular Braggwavelength. Optical controller 16 monitors the time required for theeach Bragg wavelength to return to first end 28. The time required foreach Bragg wavelength to return to first end 28 provides the location ofeach Bragg grating in first fiber optic cable 26. Having established thelocation of each Bragg grating in first fiber optic cable 26, opticaltransmitter 20 provides pulses through first fiber optic cable 26. Thewavelength of each pulse can be determined when the pulse arrives backoptical controller 16. Changes in the wavelength are detected andconverted to intensity verses time, thereby allowing optical controller16 to determine the temperature at the location of each Bragg grating infirst fiber optic cable 26.

In WDM/TDM, optical controller 16 provides optical signals through firstfiber optic cable 26 utilizing both a tunable, swept-wavelength laserand a broadband laser light source. Similar to both WDM and TDM, inWDM/TDM the reflected Bragg wavelengths are monitored for any changes inthe wavelengths. The changes in the wavelengths are converted tointensity verses time, thereby allowing optical controller 16 todetermine the temperature at the location of each Bragg grating. WDM/TDMreduces the loss of any signal in the Bragg Grating is reduced and thetotal wavelength that must be scanned to interrogate the Braggwavelength is similarly reduced.

In COFDR, optical transmitter 20 is preferably a tunable pulse laser.Fiber optic loop 18 includes first fiber optic cable 26 and a referencefiber optic cable running parallel to first fiber optic cable 26. It isunderstood that optical controller 16 may include a first opticaltransmitter dedicated to first fiber optic cable 26 and a second opticaltransmitter dedicated to the reference fiber optic cable. Both firstfiber optic cable 26 and the reference fiber optic cable 62 includeBragg gratings at the same distance within the fiber optic cable fromoptical transmitter 20. The reflected Bragg wavelengths from first fiberoptic cable 26 and the reference fiber optic cable are combined byoptical controller 16 and the combined signals are analyzed. Opticalcontroller 16 may perform an Inverse Fast Fourier Transform (IFFT) onthe fringe interference pattern to obtain the location and frequenciesof the reflected Bragg wavelengths. Temperature changes cause the Braggwavelength to shift, and the shift in the Bragg wavelength is analyzedby optical controller 16 to determine the temperature shift, and therebywhether an overheat event has occurred. In addition, the location of theoverheat event is detected by optical controller 16 based on the shiftin a particular Bragg wavelength, as the location of a Bragg gratingassociated with a Bragg wavelength is known.

Where fiber optic loop 18 is a continuous fiber optic loop, opticalcontroller 16 can analyze the optical signal using any suitable method,including Optical Time Domain Reflectometry (OTDR), COFDR, BrillouinOptical Frequency Domain Analysis (BOFDA), Brillouin Optical Time DomainAnalysis (BOTDA), Incoherent Optical Frequency Domain Reflectometry(IOFDR) utilizing a Swept Frequency Methodology, and IOFDR utilizing aStep Frequency Methodology.

In OTDR, optical controller 16 commands optical transmitter 20 to send asingle laser pulse, having a fixed wavelength, down first fiber opticcable 26. In one example, Raman scattering, which is the inelasticscattering of a photon upon interaction with matter, that occurs isutilized to determine temperature. It is understood, however, that inaddition to determining temperature along fiber optic loop 18, OTDR canbe utilized to locate the occurrence of an event at a location alongfiber optic loop 18. In Raman scattering, the scattered photons have adifferent wavelength than the incident photons. Raman scatteringincludes two types of scattering, Stokes scattering, whereby thescattered photon has a longer wavelength, and thus less energy, than theincident photon, and anti-Stokes scattering, whereby the scatteredphoton has a shorter wavelength, and thus more energy, than the incidentphoton. The intensity of the anti-Stokes band is temperature dependent,while the intensity of the Stokes band is temperature insensitive. Assuch, a ratio of the Stokes to anti-Stokes components is measured todetermine the temperature at locations along fiber optic loop 18. Thelocation of the temperature shift may be determined by the time requiredfor the backscattered photons to return to optical controller 16.

In addition to using COFDR to analyze optical signals sent through fiberoptic cables that include Bragg gratings, COFDR may be used to analyzeoptical signals sent through fiber optic cables not including Bragggratings. Similar to COFDR for fiber optic cables including Bragggratings, COFDR for fiber optic cables without Bragg gratings includesusing a fiber optic loop 18 having first fiber optic cable 26 and areference fiber optic cable running parallel to first fiber optic cable26. As the optical signal is transmitted through first fiber optic cable26, some photons are backscattered and reflected back optical controller16. Similarly, as the reference signal is transmitted through thereference cable, some reference photons are backscattered and reflectedback to optical controller 16. Optical controller 16 combines thebackscattered optical signal and the backscattered reference signal andthe combined signals create an interference pattern. Optical controller16 may perform an Inverse Fast Fourier Transform (IFFT) on a fringeinterference pattern to obtain the location and frequencies of thereflected wavelengths to create a Rayleigh fingerprint. Temperaturechanges cause the Rayleigh fingerprint to stretch, thereby shifting thereflected wavelength. The shift in the reflected wavelength is analyzedby optical controller 16 to determine temperature shift, strain shift,or both, and optical controller 16 may thereby determine whether anoverheat event has occurred.

In both BOFDA and BOTDA, an optical signal is provided to first end 28of first fiber optic cable 26 and a probe signal is simultaneouslyprovided to second end 30 of first fiber optic cable 26. Opticalcontroller 16 controls both optical transmitter 20 and a probetransmitter. Optical transmitter 20 is preferably a pump laserconfigured to provide laser pulses to first end 28 of first fiber opticcable 26. The probe transmitter provides a continuous wave to second end30 of first fiber optic cable 26. The optical signal interacts with theprobe signal, and a frequency difference between the optical signal andthe purge signal is the Brillouin frequency. Changes in the Brillouinfrequency are recorded over time, which allows optical controller 16 todetermine the temperature at a given location along first fiber opticcable 26 and determine the distance that the given location is fromfirst end 28 or second end 30. In BOFDA, optical controller 16 analyzesthe resultant Brillouin frequency with respect to frequency, while inBOTDA optical controller 16 analyzes the resultant Brillouin frequencywith respect to changes over time.

In IOFDR, a pulsed optical signal is provided to first fiber optic cable26 by optical transmitter 20. The pulsed optical signal is intensitymodulated at constant amplitude. IOFDR may utilize a swept-frequencymethodology or a step-frequency methodology. In the swept-frequencymethodology, a frequency of the optical signal provided by opticaltransmitter 20 is swept continuously across a specified frequency range.In the step-frequency methodology, the frequency of the optical signalprovided by optical transmitter 20 is altered periodically inincremental steps over a specified frequency range.

In IOFDR using either the swept-frequency methodology or thestep-frequency methodology Raman scattering is utilized to determine thetemperature along first fiber optic cable 26. As discussed above, Ramanscattering includes two component types of scattering, a Stokescomponent and an anti-Stokes component. The Stokes component includesscattered photons that have a longer wavelength, and thus less energy,than the incident photon. The anti-Stokes component includes scatteredphotons that have a shorter wavelength, and thus more energy, than theincident photon. The anti-Stokes component is temperature dependent,while the Stokes band is temperature insensitive. The intensity of thebackscattered Raman signal, which is a combination of Stokes andanti-Stokes components, is measured as a function of frequency. Opticalcontroller 16 performs an IFFT to convert the signal frequency to thespace domain, from which the temperature is calculated. The ratio ofStokes to anti-Stokes intensities eliminates any non-temperature relatedvariations to the signal, thereby giving a temperature readingunaffected by noise.

DISCUSSION OF POSSIBLE EMBODIMENTS

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A system configured to monitor temperature in a plurality of zones of anaircraft can include a first fiber optic cable routed through each ofthe plurality of zones of the aircraft system, an optical transmitterconfigured to provide an optical signal to the first fiber optic cable,an optical receiver configured to receive an optical response from thefirst fiber optic cable, and a controller operatively connected to theoptical receiver and configured to determine at least one temperaturefor each of the plurality of zones based on the optical response andoutput an indication for detected zones of the plurality of zones inwhich the at least one temperature is greater than a threshold value.

The system of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

The first fiber optic cable can include fiber Bragg gratings.

The controller can be configured to control the optical transmitter anddetermine the at least one temperature for each of the plurality ofzones using time division multiplexing (TDM) and/or wavelength divisionmultiplexing (WDM).

The system can further include a second fiber optic cable can be routedthrough the plurality of zones parallel to the first fiber optic cable,and the controller can be configured to provide a reference signal tothe second fiber optic cable and receive a reference response from thesecond fiber cable.

The controller can be configured to determine the at least onetemperature in each of the plurality of zones based upon the referenceresponse, the optical response, and coherent optical frequency domainreflectometry (COFDR).

The first and second fiber optic cables can include fiber Bragggratings.

The optical transmitter can be configured to produce laser pulses with aconstant amplitude, and wherein the controller implements IncoherentOptical Frequency Domain Reflectometry (IOFDR) with a step frequency orswept frequency methodology.

The controller can be configured to control the optical transmitter toprovide the optical signal as a single laser pulse at a fixedwavelength, and the controller can be configured to determine the atleast one temperature of each of the plurality of zones using opticaltime domain reflectometry (OTDR).

The optical transmitter can be connected to provide the optical signalto a first end of the first fiber optic cable and the optical receivercan be connected to receive the optical response from a second end ofthe first fiber optic cable, the system can further include a probetransmitter connected to the second end of the first fiber optic cableand configured to provide a probe signal to the second end of the firstfiber optic cable, and a probe receiver connected to the first end ofthe first fiber optic cable and configured to receive the probe signalfrom the first end of the first fiber optic cable, and the controllercan be configured to determine the at least one temperature of each ofthe plurality of zones based on a frequency difference between theoptical response and the probe response using Brillouin optical timedomain analysis (BOTDA).

The aircraft system can be a bleed air system, and the plurality ofzones comprise bleed air ducts.

At least one of the plurality of zones can comprise a wheel well of theaircraft, and a physical condition of the wheel well can be determinedby the controller to determine a temperature of a landing gear tire.

A method of detecting thermal conditions for a plurality of zones of anaircraft system can include emitting, by an optical transmitter, anoptical signal to a first fiber optic cable, wherein the first fiberoptic cable is routed through each of the plurality of zones of theaircraft system, receiving, by an optical receiver, a response signalfrom the first fiber optic cable based upon the optical signal,determining, using a controller, at least one temperature of each of theplurality of zones based upon the response signal, and indicating adetected condition for detected zones of the plurality of zones in whichthe at least one temperature is greater than a threshold.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

The first fiber optic cable can include fiber Bragg gratings, andwherein emitting, by the optical transmitter, the optical signal caninclude emitting the optical signal using a tunable, swept-wavelengthlaser; and wherein determining, using the controller, the at least onetemperature for each of the plurality of zones comprises determining theat least one temperature based on wavelength division multiplexing(WDM).

The first fiber optic cable can include fiber Bragg gratings, andwherein emitting, by the optical transmitter, the optical signalcomprises emitting the optical signal using a broadband laser; andwherein determining, using the controller, the at least one temperatureof each of the plurality of zones comprises determining the at least onetemperature based on time division multiplexing (TDM).

Emitting, by the optical transmitter, the optical signal can includeemitting laser pulses having a constant amplitude using a step frequencymethodology; and wherein determining, using the controller, the at leastone temperature of each of the plurality of zones can includedetermining the at least one temperature based on optical frequencydomain reflectometry (IOFDR).

Emitting, by the optical transmitter, the optical signal can includeemitting laser pulses having a constant amplitude using a sweptfrequency methodology; and wherein determining, using the controller,the at least one temperature for each of the plurality of zones caninclude determining the at least one temperature based on opticalfrequency domain reflectometry (IOFDR).

The method can further include providing a reference signal to a secondfiber optic cable routed parallel to the first fiber optic cable throughthe plurality of zones, and receiving a reference response from thesecond fiber cable based on the reference signal, wherein determining,using the controller, the at least one temperature of each of theplurality of zones can include determining the at least one temperaturebased upon the reference response, the optical response, and coherentoptical frequency domain reflectometry (COFDR).

The first and second fiber optic cables can include fiber Bragggratings.

Emitting, by the optical transmitter, the optical signal can includeemitting the optical signal as a single laser pulse at a fixedwavelength, and determining, using the controller, the at least onetemperature of each of the plurality of zones can include determiningthe at least one temperature for each of the plurality of zones usingoptical time domain reflectometry (OTDR).

Emitting, by the optical transmitter, the optical signal can includeemitting the optical signal to a first end of the first fiber opticcable, and receiving, by the optical receiver, the response signal caninclude receiving the optical response from a second end of the firstfiber optic cable, and the method can further include emitting, by aprobe transmitter, a probe signal to the second end of the first fiberoptic cable, and receiving, by a probe receiver, a probe response fromthe first end of the first fiber optic cable, and where determining,using the controller, the at least one temperature of each of theplurality of zones can include determining the at least one temperatureof each of the plurality of zones based on a frequency differencebetween the optical response and the probe response using Brillouinoptical time domain analysis (BOTDA).

An system for an aircraft having at least one zone can include a firstzone fiber optic cable routed through a first zone of the at least onezone, a first local controller configured to provide an optical signalto the first zone fiber optic cable and obtain a response signal fromthe first zone fiber optic cable, wherein the first local controller isconfigured to determine at least one temperature for the first zonebased on the response signal and provide an indication for the firstzone if the at least one temperature for the first zone is greater thana threshold value.

The overheat detection system of the preceding paragraph can optionallyinclude, additionally and/or alternatively, any one or more of thefollowing features, configurations and/or additional components:

The system can further include a second zone of the at least one zonethat includes a second zone fiber optic cable and a second localcontroller, and a main controller configured to communicate with thefirst controller and the second controller.

The first zone fiber optic cable can include fiber Bragg gratings.

The first local controller can be configured to control an opticaltransmitter to provide the optical signal as a tunable swept-wavelengthlaser and/or a broadband laser and is configured to determine the atleast one temperature for each of the first zone using time divisionmultiplexing (TDM) and/or wavelength division multiplexing (WDM).

The system can further include a reference fiber optic cable routedthrough the first zone parallel to the first zone fiber optic cable,wherein the first local controller can be configured to provide areference signal to the reference fiber optic cable and receive areference response from the reference fiber cable.

The first local controller can be configured to determine the at leastone temperature of the first zone based upon the reference response, theresponse signal, and coherent optical frequency domain reflectometry(COFDR).

The first zone fiber optic cable and the reference fiber optic cable caninclude fiber Bragg gratings.

The first local controller can include an optical transmitter that isconfigured to produce laser pulses with a constant amplitude, whereinthe first local controller can implement Incoherent Optical FrequencyDomain Reflectometry (IOFDR) with a step frequency or swept frequencymethodology.

The first local controller can include an optical transmitter configuredto provide the optical signal as a single laser pulse at a fixedwavelength, wherein the local controller is can be configured todetermine the at least one temperature of the first zone using opticaltime domain reflectometry (OTDR).

The first local controller can be configured to provide the opticalsignal to a first end of the first zone fiber optic cable and the firstlocal controller can be configured to receive the response signal from asecond end of the first zone fiber optic cable, and wherein the firstlocal controller can be further configured to provide a probe signal tothe second end of the first zone fiber optic cable and receive the probesignal from the first end of the first zone fiber optic cable, andwherein the first local controller can be configured to determine thetemperature of the first zone based on a frequency difference betweenthe response signal and the probe response using Brillouin optical timedomain analysis (BOTDA).

The first zone can be a bleed air duct, cross-over bleed air duct, wheelwell, wing box, air conditioning system, anti-icing system or nitrogengeneration system.

A method of detecting thermal conditions for a zone of an aircraftsystem can include emitting, by a local controller, an optical signal toa zone fiber optic cable, wherein the zone fiber optic cable is routedthrough the zone of the aircraft system, receiving, by the localcontroller, a response signal from the zone fiber optic cable based uponthe optical signal, determining, using the local controller, at leastone temperature of the zone based upon the response signal, andindicating a condition for the zone if the at least one temperature forthe zone is greater than a threshold.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

Indicating the overheat condition can include indicating the overheatcondition to an avionics controller of the aircraft.

The zone fiber optic cable can include fiber Bragg gratings, andemitting, by the local controller, the optical signal can includeemitting the optical signal using a tunable, swept-wavelength laser, andwherein determining, using the local controller, the at least onetemperature of the zone can include determining the at least onetemperature based on wavelength division multiplexing (WDM).

The zone fiber optic cable can include fiber Bragg gratings, andemitting, by the local controller, the optical signal can includeemitting the optical signal using a broadband laser, and whereindetermining, using the controller, the at least one temperature of thezone can include determining the at least one temperature based on timedivision multiplexing (TDM).

Emitting, by the local controller, the optical signal can includeemitting laser pulses having a constant amplitude using a step frequencymethodology, and determining, using the local controller, the at leastone temperature of the zone can include determining the at least onetemperature based on optical frequency domain reflectometry (IOFDR).

Emitting, by the local controller, the optical signal can includeemitting laser pulses having a constant amplitude using a sweptfrequency methodology, and determining, using the local controller, theat least one temperature of the zone can include determining the atleast one temperature based on optical frequency domain reflectometry(IOFDR).

The method can further include providing a reference signal to a secondfiber optic cable configured to run parallel to the zone fiber opticcable through the zone, and receiving a reference response from thesecond fiber cable based on the reference signal, wherein determining,using the local controller, the at least one temperature of the zone caninclude determining the at least one temperature based upon thereference response, the response signal, and coherent optical frequencydomain reflectometry (COFDR).

Emitting, by the local controller, the optical signal can includeemitting the optical signal as a single laser pulse at a fixedwavelength, wherein determining, using the local controller, the atleast one temperature of the zone can include determining the at leastone temperature of each of the zone using optical time domainreflectometry (OTDR).

Emitting, by the local controller, the optical signal can includeemitting the optical signal to a first end of the first fiber opticcable, and receiving, by the local controller, the response signal caninclude receiving the response signal from a second end of the firstfiber optic cable, and the method can further include providing a probesignal to the second end of the first fiber optic cable, and receiving aprobe response from the first end of the first fiber optic cable, andwherein determining, using the local controller, the at least onetemperature of the zone can include determining the at least onetemperature of the zone based on a frequency difference between theresponse signal and the probe response using Brillouin optical timedomain analysis (BOTDA).

A system for an aircraft that includes a plurality of zones includes afirst zone fiber optic cable routed through a first set of the pluralityof zones, a first local controller configured to provide a first opticalsignal to the first zone fiber optic cable and obtain a first responsesignal from the first zone fiber optic cable, and wherein the firstlocal controller is further configured to determine at least onetemperature for each of first set of the plurality of zones based on thefirst response signal and provide an indication for first detected zonesof the first set of the plurality of zones in which the at least onetemperature is greater than a threshold value.

The overheat detection system of the preceding paragraph can optionallyinclude, additionally and/or alternatively, any one or more of thefollowing features, configurations and/or additional components:

The system can further include a second zone fiber optic cable routedthrough a second set of the plurality of zones, a second localcontroller configured to provide a second optical signal to the secondzone fiber optic cable and obtain a second response signal from thesecond zone fiber optic cable, and wherein the second local controlleris further configured to determine at least one temperature for each ofthe second set of the plurality of zones based on the second responsesignal and provide an indication for second detected zones of the secondset of the plurality of zones in which the at least one temperature isgreater than a threshold value.

The system can further include a main controller configured tocommunication with the first and second local controllers, wherein thefirst and second local controllers provide the indication for the firstand second detected zones to the main controller.

The first zone fiber optic cable can include fiber Bragg gratings, andthe first local controller can be configured to control an opticaltransmitter to provide the optical signal as a tunable swept-wavelengthlaser and/or a broadband laser and can be configured to determine the atleast one temperature for each of the first set of the plurality ofzones using time division multiplexing (TDM) and/or wavelength divisionmultiplexing (WDM).

The system can further include a reference fiber optic cable routedthrough each of the first set of the plurality of zones parallel to thefirst zone fiber optic cable, and wherein the first local controller canbe configured to provide a reference signal to the reference fiber opticcable and receive a reference response from the reference fiber cable.

The first local controller can be configured to determine the at leastone temperature of each of the first set of the plurality of zones basedupon the reference response, the optical response, and coherent opticalfrequency domain reflectometry (COFDR).

The first zone fiber optic cable and the reference fiber optic cable caninclude fiber Bragg gratings.

The first local controller can include an optical transmitter that isconfigured to produce laser pulses with a constant amplitude, andwherein the first local controller can implement Incoherent OpticalFrequency Domain Reflectometry (IOFDR) with a step frequency or sweptfrequency methodology.

The first local controller can include an optical transmitter configuredto provide the first optical signal as a single laser pulse at a fixedwavelength, and wherein the first local controller can be configured todetermine the at least one temperature of each of the first set of theplurality of zones using optical time domain reflectometry (OTDR).

The first local controller can be configured to provide the firstoptical signal to a first end of the first zone fiber optic cable andthe first local controller can be configured to receive the firstresponse signal from a second end of the first zone fiber optic cable,and wherein the first local controller can be further configured toprovide a probe signal to the second end of the first zone fiber opticcable and receive the probe signal from the first end of the first zonefiber optic cable, and wherein the first local controller can beconfigured to determine the at least one temperature for each of thefirst set of the plurality of zones based on a frequency differencebetween the response signal and the probe response using Brillouinoptical time domain analysis (BOTDA).

Each of the first set of the plurality of zones can be one of a bleedair duct, cross-over bleed air duct, wheel well, wing box, airconditioning system, anti-icing system or nitrogen generation system.

A method of detecting thermal conditions for an aircraft can includeemitting, by a first local controller, a first optical signal to a firstzone fiber optic cable, wherein the first zone fiber optic cable isrouted through each of a first plurality of zones of the aircraft,receiving, by the first local controller, a response signal from thefirst zone fiber optic cable based upon the first optical signal,determining, using the first local controller, at least one temperaturefor each of the first plurality of zones based on the response signal,and indicating a first condition for a respective one of the firstplurality of zones if the at least one temperature for the respectiveone of the first plurality of zones is greater than a threshold.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

The method can further include emitting, by a second local controller, asecond optical signal to a second zone fiber optic cable, wherein thesecond zone fiber optic cable is routed through each of a secondplurality of zones of the aircraft, receiving, by the second localcontroller, a response signal from the second zone fiber optic cablebased upon the second optical signal, determining, using the secondlocal controller, at least one temperature for each of the secondplurality of zones based on the response signal, and indicating a secondcondition for a respective one of the second plurality of zones if theat least one temperature for the respective one of the second pluralityof zones is greater than a threshold.

Indicating the first condition can include indicating the firstcondition to an avionics controller of the aircraft, and whereinindicating the second condition can include indicating the secondcondition to the avionics controller.

The first zone fiber optic cable can include fiber Bragg gratings, andemitting, by the first local controller, the first optical signal caninclude emitting the first optical signal using a tunable,swept-wavelength laser, and wherein determining, using the first localcontroller, the at least one temperature each of the plurality of zonescan include determining the at least one temperature based on wavelengthdivision multiplexing (WDM).

The first zone fiber optic cable can include fiber Bragg gratings, andemitting, by the first local controller, the first optical signal caninclude emitting the first optical signal using a broadband laser, anddetermining, using the first local controller, the at least onetemperature of each of the first plurality of zones can includedetermining the at least one temperature based on time divisionmultiplexing (TDM).

Emitting, by the first local controller, the first optical signal caninclude emitting laser pulses having a constant amplitude using a stepfrequency methodology, and determining, using the first localcontroller, the at least one temperature of each of the first pluralityof zones can include determining the at least one temperature based onoptical frequency domain reflectometry (IOFDR).

Emitting, by the first local controller, the first optical signal caninclude emitting laser pulses having a constant amplitude using a sweptfrequency methodology, and determining, using the first localcontroller, the at least one temperature of each of the first pluralityof zones can include determining the at least one temperature based onoptical frequency domain reflectometry (IOFDR).

The method can further include providing a reference signal to a secondfiber optic cable configured to run parallel to the first zone fiberoptic cable through each of the first plurality of zones, and receivinga reference response from the second fiber cable based on the referencesignal, wherein determining, using the first local controller, the atleast one temperature of each of the first plurality of zones caninclude determining the at least one temperature based upon thereference response, the first optical response, and coherent opticalfrequency domain reflectometry (COFDR).

Emitting, by the first local controller, the first optical signal caninclude emitting the first optical signal to a first end of the firstzone fiber optic cable, and wherein receiving, by the first localcontroller, the response signal can include receiving the first opticalresponse from a second end of the first zone fiber optic cable, and themethod can further include providing a probe signal to the second end ofthe first zone fiber optic cable, and receiving a probe response fromthe first end of the first zone fiber optic cable, and whereindetermining, using the first local controller, the at least onetemperature of each of the first plurality of zones can includedetermining the at least one temperature based on a frequency differencebetween the first optical response and the probe response usingBrillouin optical time domain analysis (BOTDA).

A health monitoring system of an aircraft can include a first fiberoptic cable routed through at least one zone of the aircraft, an opticaltransmitter configured to provide an optical signal to the first fiberoptic cable, an optical receiver configured to receive an opticalresponse from the first fiber optic cable, and a controller operativelyconnected to the optical receiver and configured to determine a physicalcharacteristic for the at least one zone based on the optical response,and store a plurality of values of the physical characteristic over atime period in a memory.

The health monitoring system of the preceding paragraph can optionallyinclude, additionally and/or alternatively, any one or more of thefollowing features, configurations and/or additional components:

The first fiber optic cable can include fiber Bragg gratings.

The controller can be configured to control the optical transmitter anddetermine the physical characteristic for the at least one zone usingtime division multiplexing (TDM) and/or wavelength division multiplexing(WDM).

The system can further include a second fiber optic cable routed throughthe at least one zone parallel to the first fiber optic cable, whereinthe controller can be configured to provide a reference signal to thesecond fiber optic cable and receive a reference response from thesecond fiber cable.

The controller can be configured to determine the physicalcharacteristic based upon the reference response, the optical response,and coherent optical frequency domain reflectometry (COFDR).

The first and second fiber optic cables can include fiber Bragggratings.

The optical transmitter can be configured to produce laser pulses with aconstant amplitude, and wherein the controller can implement IncoherentOptical Frequency Domain Reflectometry (IOFDR) with a step frequency orswept frequency methodology.

The controller can be configured to control the optical transmitter toprovide the optical signal as a single laser pulse at a fixedwavelength, and wherein the controller can be configured to determinethe physical characteristic of the at least one zone using optical timedomain reflectometry (OTDR).

The optical transmitter can be connected to provide the optical signalto a first end of the first fiber optic cable and the optical receivercan be connected to receive the optical response from a second end ofthe first fiber optic cable, and the system can further include a probetransmitter connected to the second end of the first fiber optic cableand configured to provide a probe signal to the second end of the firstfiber optic cable, and a probe receiver connected to the first end ofthe first fiber optic cable and configured to receive the probe signalfrom the first end of the first fiber optic cable, wherein thecontroller can be configured to determine the physical characteristic ofthe at least one zone based on a frequency difference between theoptical response and the probe response using Brillouin optical timedomain analysis (BOTDA).

The at least one zone can be one of a bleed air duct, cross-over bleedair duct, wheel well, wing box, air conditioning system, anti-icingsystem or nitrogen generation system.

The physical characteristic can be a temperature or a strain.

A method of monitoring the health of an aircraft can include emitting,by an optical transmitter, an optical signal to a first fiber opticcable, wherein the first fiber optic cable is routed through at leastone zone of the aircraft, receiving, by an optical receiver, a responsesignal from the first fiber optic cable based upon the optical signal,determining, using a controller, a physical characteristic of the atleast one zone, storing, in a memory, a plurality of values of thephysical characteristic for the at least one zone, and determining atrend for the physical characteristic based on the plurality of values.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

The first fiber optic cable can include fiber Bragg gratings, whereinemitting, by the optical transmitter, the optical signal can includeemitting the optical signal using a tunable, swept-wavelength laser, andwherein determining, using the controller, the physical characteristicof the at least one zone can include determining the physicalcharacteristic based on wavelength division multiplexing (WDM).

The first fiber optic cable can include fiber Bragg gratings, andwherein emitting, by the optical transmitter, the optical signal caninclude emitting the optical signal using a broadband laser, and whereindetermining, using the controller, the physical characteristic of the atleast one zone can include determining the physical characteristic basedon time division multiplexing (TDM).

Emitting, by the optical transmitter, the optical signal can includeemitting laser pulses having a constant amplitude using a step frequencymethodology, and determining, using the controller, the physicalcharacteristic of the at least one zone can include determining thephysical characteristic based on optical frequency domain reflectometry(IOFDR).

Emitting, by the optical transmitter, the optical signal can includeemitting laser pulses having a constant amplitude using a sweptfrequency methodology, and determining, using the controller, thephysical characteristic of the at least one zone can include determiningthe physical characteristic based on optical frequency domainreflectometry (IOFDR).

The method can further include providing a reference signal to a secondfiber optic cable configured to run parallel to the first fiber opticcable through the at least one zone, and receiving a reference responsefrom the second fiber cable based on the reference signal, whereindetermining, using the controller, the physical characteristic of the atleast one zone can include determining the physical characteristic basedupon the reference response, the optical response, and coherent opticalfrequency domain reflectometry (COFDR).

The first and second fiber optic cables can include fiber Bragggratings.

Emitting, by the optical transmitter, the optical signal can includeemitting the optical signal as a single laser pulse at a fixedwavelength, and determining, using the controller, the physicalcharacteristic of the at least one zone can include determining thephysical characteristic of the at least one zone using optical timedomain reflectometry (OTDR).

Emitting, by the optical transmitter, the optical signal can includeemitting the optical signal to a first end of the first fiber opticcable, and receiving, by the optical receiver, the response signal caninclude receiving the optical response from a second end of the firstfiber optic cable, and the method can further include providing, by aprobe transmitter, a probe signal to the second end of the first fiberoptic cable, and receiving, by a probe receiver, a probe response fromthe first end of the first fiber optic cable, wherein determining, usingthe controller, the physical characteristic of the at least one zone caninclude determining the physical characteristic of the at least one zonebased on a frequency difference between the optical response and theprobe response using Brillouin optical time domain analysis (BOTDA).

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A system for an aircraft that includes a plurality of zones, thesystem comprising: a first zone fiber optic cable routed through a firstset of the plurality of zones; a first local controller configured toprovide a first optical signal to the first zone fiber optic cable andobtain a first response signal from the first zone fiber optic cable;wherein the first local controller is further configured to determine atleast one temperature for each of first set of the plurality of zonesbased on the first response signal and provide an indication for firstdetected zones of the first set of the plurality of zones in which theat least one temperature is greater than a threshold value.
 2. Thesystem of claim 1, further comprising: a second zone fiber optic cablerouted through a second set of the plurality of zones; a second localcontroller configured to provide a second optical signal to the secondzone fiber optic cable and obtain a second response signal from thesecond zone fiber optic cable; wherein the second local controller isfurther configured to determine at least one temperature for each of thesecond set of the plurality of zones based on the second response signaland provide an indication for second detected zones of the second set ofthe plurality of zones in which the at least one temperature is greaterthan a threshold value.
 3. The system of claim 2, further comprising: amain controller configured to communication with the first and secondlocal controllers, wherein the first and second local controllersprovide the indication for the first and second detected zones to themain controller.
 4. The system of claim 1, wherein the first zone fiberoptic cable includes fiber Bragg gratings, and wherein the first localcontroller is configured to control an optical transmitter to providethe optical signal as a tunable swept-wavelength laser and/or abroadband laser and is configured to determine the at least onetemperature for each of the first set of the plurality of zones usingtime division multiplexing (TDM) and/or wavelength division multiplexing(WDM).
 5. The system of claim 1, further comprising: a reference fiberoptic cable routed through each of the first set of the plurality ofzones parallel to the first zone fiber optic cable; wherein the firstlocal controller is configured to provide a reference signal to thereference fiber optic cable and receive a reference response from thereference fiber cable.
 6. The system of claim 5, wherein the first localcontroller is configured to determine the at least one temperature ofeach of the first set of the plurality of zones based upon the referenceresponse, the optical response, and coherent optical frequency domainreflectometry (COFDR).
 7. The system of claim 6, wherein the first zonefiber optic cable and the reference fiber optic cable include fiberBragg gratings.
 8. The system of claim 1, wherein the first localcontroller includes an optical transmitter that is configured to producelaser pulses with a constant amplitude, and wherein the first localcontroller implements Incoherent Optical Frequency Domain Reflectometry(IOFDR) with a step frequency or swept frequency methodology.
 9. Thesystem of claim 1, wherein the first local controller includes anoptical transmitter configured to provide the first optical signal as asingle laser pulse at a fixed wavelength, and wherein the first localcontroller is configured to determine the at least one temperature ofeach of the first set of the plurality of zones using optical timedomain reflectometry (OTDR).
 10. The system of claim 1, wherein thefirst local controller is configured to provide the first optical signalto a first end of the first zone fiber optic cable and the first localcontroller is configured to receive the first response signal from asecond end of the first zone fiber optic cable, and wherein the firstlocal controller is further configured to provide a probe signal to thesecond end of the first zone fiber optic cable and receive the probesignal from the first end of the first zone fiber optic cable, andwherein the first local controller is configured to determine the atleast one temperature for each of the first set of the plurality ofzones based on a frequency difference between the response signal andthe probe response using Brillouin optical time domain analysis (BOTDA).11. The system of claim 1, wherein the each of the first set of theplurality of zones is one of a bleed air duct, cross-over bleed airduct, wheel well, wing box, air conditioning system, anti-icing systemor nitrogen generation system.
 12. A method of detecting thermalconditions for an aircraft, the method comprising: emitting, by a firstlocal controller, a first optical signal to a first zone fiber opticcable, wherein the first zone fiber optic cable is routed through eachof a first plurality of zones of the aircraft; receiving, by the firstlocal controller, a response signal from the first zone fiber opticcable based upon the first optical signal; determining, using the firstlocal controller, at least one temperature for each of the firstplurality of zones based on the response signal; and indicating a firstcondition for a respective one of the first plurality of zones if the atleast one temperature for the respective one of the first plurality ofzones is greater than a threshold.
 13. The method of claim 12, furthercomprising: emitting, by a second local controller, a second opticalsignal to a second zone fiber optic cable, wherein the second zone fiberoptic cable is routed through each of a second plurality of zones of theaircraft; receiving, by the second local controller, a response signalfrom the second zone fiber optic cable based upon the second opticalsignal; determining, using the second local controller, at least onetemperature each of the second plurality of zones based on the responsesignal; and indicating a second condition for a respective one of thesecond plurality of zones if the at least one temperature for therespective one of the second plurality of zones is greater than athreshold.
 14. The method of claim 13, wherein indicating the firstcondition comprises indicating the first condition to an avionicscontroller of the aircraft, and wherein indicating the second conditioncomprises indicating the second condition to the avionics controller.15. The method of claim 12, wherein the first zone fiber optic cableincludes fiber Bragg gratings, and wherein emitting, by the first localcontroller, the first optical signal comprises emitting the firstoptical signal using a tunable, swept-wavelength laser; and whereindetermining, using the first local controller, the at least onetemperature of each of the plurality of zones comprises determining theat least one temperature based on wavelength division multiplexing(WDM).
 16. The method of claim 12, wherein the first zone fiber opticcable includes fiber Bragg gratings, and wherein emitting, by the firstlocal controller, the first optical signal comprises emitting the firstoptical signal using a broadband laser; and wherein determining, usingthe first local controller, the at least one temperature of each of thefirst plurality of zones comprises determining the at least onetemperature based on time division multiplexing (TDM).
 17. The method ofclaim 12, wherein emitting, by the first local controller, the firstoptical signal comprises emitting laser pulses having a constantamplitude using a step frequency methodology; and wherein determining,using the first local controller, the at least one temperature of eachof the first plurality of zones comprises determining the at least onetemperature based on optical frequency domain reflectometry (IOFDR). 18.The method of claim 12, wherein emitting, by the first local controller,the first optical signal comprises emitting laser pulses having aconstant amplitude using a swept frequency methodology; and whereindetermining, using the first local controller, the at least onetemperature of each of the first plurality of zones comprisesdetermining the at least one temperature based on optical frequencydomain reflectometry (IOFDR).
 19. The method of claim 12, furthercomprising: providing a reference signal to a second fiber optic cableconfigured to run parallel to the first zone fiber optic cable througheach of the first plurality of zones; and receiving a reference responsefrom the second fiber cable based on the reference signal; whereindetermining, using the first local controller, the at least onetemperature of each of the first plurality of zones comprisesdetermining the at least one temperature based upon the referenceresponse, the first optical response, and coherent optical frequencydomain reflectometry (COFDR).
 20. The method of claim 12, whereinemitting, by the first local controller, the first optical signalcomprises emitting the first optical signal to a first end of the firstzone fiber optic cable, and wherein receiving, by the first localcontroller, the response signal comprises receiving the first opticalresponse from a second end of the first zone fiber optic cable, andwherein the method further comprises: providing a probe signal to thesecond end of the first zone fiber optic cable; and receiving a proberesponse from the first end of the first zone fiber optic cable; whereindetermining, using the first local controller, the at least onetemperature of each of the first plurality of zones comprisesdetermining the at least one temperature based on a frequency differencebetween the first optical response and the probe response usingBrillouin optical time domain analysis (BOTDA).